An Atlas of Cerulean Warbler Populations - Cornell Lab of Ornithology

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METHODSCEWAP took advantage of the expertise of activebirders and professional biologists by employing networksof volunteers. The Lab of Ornithology hired fieldassistants in 1997, 1998, and 1999 to cover areas thoughtto be potentially important breeding areas for ceruleans.These specific areas within states were systematicallysearched; however, coverage of entire states was oftenstill incomplete.Field protocols consisted primarily of surveyingknown sites (determined through state atlas workers,other birders, and published literature) to determinenumbers of pairs, breeding status of population, andconservation status of site. In addition, participants surveyedas many new or potential sites as possible, to identifynew breeding sites and determine status (as in thefirst project goal). At a small subset of sites with largeor important populations, additional data on nesting andforaging, as well as productivity and threats to populations,was available through collaborating researchers.Because of our reliance on volunteers and unsupervisedfield assistants, and the large differences in terrainand habitats surveyed, there was much variation inactual survey methods employed in the field. A majorityof data came from variations on the “area-search”method, where observers moved through potential habitatsnoting presence and numbers of singing male CeruleanWarblers. Variations ranged from systematic surveysalong all navigable waterways by canoe in theMontezuma Wetlands Complex of NY (Bill Evans), todriving slowly along rural roads in northern NJ (JohnBenzinger), to hiking the Appalachian Trail in Virginia andNorth Carolina, to floating stretches of several rivers inMissouri, to systematically driving and hiking throughforested regions and conducting point counts whereverceruleans were detected (David Buehler), to spot-checkingisolated woodlots. Field surveys often used recordedCerulean Warbler vocalizations (as needed) to elicit responsesfrom territorial males, approximate territorialboundaries (especially in linear habitats), and determinepairing status (females often respond to tapes within theirterritories). After visits to a site were completed, observerswere asked to attempt an estimate of the totalbreeding population of Cerulean Warblers at that site.In addition to these CEWAP surveys, we receivedseveral datasets with point-count locations for CeruleanWarblers, often detected during more general bird surveys.In these cases, it is often impossible to know howmuch available habitat was covered or what proportionof a regional population of Cerulean Warblers wassampled—these are retained in our Atlas as minimumestimates for these areas. In a few states we relied onadditional surveys conducted prior to CEWAP or as partof independent research efforts. Finally, some holes inour Atlas were filled by gleaning miscellaneous recordsfrom birding e-mail lists, recently published BreedingBird Atlases, or by hounding certain birders and statebiologists until they told us what they knew.We instructed participants to define a “site” as anycontiguous patch of similar and suitable habitat surroundedby a different habitat type. Because of the greatvariation in survey methods and types of data we received,the actual designation of sites in our database ishighly inconsistent. These range from specific locationsof individual Cerulean Warblers within a larger contiguousarea, to politically defined State Park or WildlifeManagement Area boundaries, to entire river valleyswith their adjacent slopes. In all cases; however, a “site”represents a unique latitude and longitude provided bya participant and entered into our database. Althoughthis variation leads to difficulties in interpreting numbersor proportions of sites occupied in various regionsor states, this flexibility in our protocols enabled us toreceive the maximum amount of data from the widestgroup of volunteers and collaborators.All sites were located on topographic maps, and dataon habitat, landscape characteristics, and land ownershipwere noted on simple data forms. Specifically, fieldobservers recorded site location, latitude and longitude,elevation, history of disturbance, general habitat type(riparian, swamp forest, dry slope, etc.), three or moredominant tree species, and canopy height. This informationwas compiled and entered into a GIS databaseby Lab of Ornithology biologists.4
Range-wide SummaryA total of 280 CEWAP participants and collaboratorsreported data on Cerulean Warblers; these included29 paid field assistants hired over the 3-year period(Table 1; see also Appendix 1 for complete list ofCEWAP participants). The sum of data we received accountedfor 7,669 Cerulean Warblers at 1,923 sites in28 states, plus Ontario. Virtually all reports were of singingmales; therefore numbers reported throughout thisRESULTSAtlas are assumed to represent number of territorialmales or breeding pairs. An additional 355 sites weresearched with no birds found; in general observers onlyreported positive sightings, and these do not representrandom samples of available areas or habitats. Note too,that “sites” ranged in scope from individual point-locationsto whole river valleys, so these data provide onlya rough indication of number of different areas that supportCerulean Warbler populations.Table 1. Summary of CEWAP participants, numbers of sites, and number of Cerulean Warblers reported, by state,1997–1999.State Number Number Number Number Numberof participants returning of sites of sites of birdssigned up data surveyed with birds foundAlabama 7 1 6 6 7Arkansas 12 4 48 46 145Connecticut 22 7 20 13 34District of Columbia 4 0 - - -Delaware 6 2 7 7 10Georgia 18 5 16 14 22Iowa 9 2 9 9 22Illinois 26 3 32 21 1000+Indiana 22 8 73 34 342Kansas 1 1 1 1 1Kentucky 17 8 113 59 140Massachusetts 22 6 11 10 18Maryland 17 6 11 9 16Maine 4 0 - - -Michigan 36 15 183 176 507Minnesota 17 4 57 57 103Missouri 14 5 32 31 301Mississippi 2 0 - - -Nebraska 2 1 1 1 1New Hampshire 5 0 - - -New Jersey 18 7 32 31 157New York 159 57 286 246 1068North Carolina 19 12 42 39 109Ohio 46 17 78 62 264Oklahoma 2 0 - - -Ontario 9 1 5 4 228Pennsylvania 81 38 206 182 548Rhode Island 3 1 1 0 0South Carolina 3 0 - - -South Dakota 2 2 2 2 3Tennessee 27 14 488 485 1210Virginia 48 15 106 64 152Vermont 13 2 4 3 3Wisconsin 25 10 60 59 174West Virginia 68 27 345 254 1124TOTALS 786 280 2274 1923 76695
Page 1: AN ATLAS OFCERULEAN WARBLER POPULAT
Page 6 and 7: The scope and distribution of range
Page 8 and 9: Table 3. Areas supporting moderate-
Page 10 and 11: Number of occupied sitesRegion 3—
Page 12 and 13: Number of occupied sitesNumber of o
Page 14 and 15: CEWAP Populations in Arkansas, 1997
Page 16 and 17: CT Habitats (N=14)CT Tree Species (
Page 18 and 19: CEWAP Populations in Illinois, 1997
Page 20 and 21: Although only 7 (21%) of the 34 sit
Page 22 and 23: CEWAP Populations in Kentucky, 1997
Page 24 and 25: CEWAP Populations in Maryland, 1997
Page 26 and 27: MI Habitats (N=175)MI Tree Species
Page 28 and 29: MissouriThe Missouri Breeding Bird
Page 30 and 31: NebraskaCEWAP participants surveyed
Page 32 and 33: patches, the apparent sites of aban
Page 34 and 35: lers in New York State has been des
Page 36 and 37: irds were located at other points a
Page 38 and 39: areas were at opposite ends of the
Page 40 and 41: The most commonly reported tree spe
Page 42 and 43: A third important region of the sta
Page 44 and 45: VA Habitats (N=60)VA Tree Species (
Page 46 and 47: River and Wyalusing State Park in G
Page 48 and 49: Table 20. Important areas for breed
Page 50 and 51: DISCUSSION AND CONCLUSIONSThe Cerul
Page 52 and 53: medium-sized waterways. Only a few
Page 54 and 55:
LITERATURE CITEDAndrle, R. F., and
Page 56:
APPENDIXAppendix 1. List of CEWAP p
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An Atlas of Cerulean Warbler Populations - Cornell Lab of Ornithology

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